c - Determining button boundries with terminal IO in non-canonical mode -


i'm trying understand how terminal i/o works.

when terminal placed in non-canonical mode (missing error handling):

struct termios term_original, term_current; tcgetattr(stdin_fileno, &term_original); term_current = term_original; term_current.c_lflag &= ~(icanon | isig | iexten | echo); term_current.c_iflag &= ~(brkint | icrnl | ignbrk | igncr | inlcr | inpck | istrip | ixon | parmrk); term_current.c_oflag &= ~(opost); term_current.c_cc[vmin]  = 1; term_current.c_cc[vtime] = 0; tcsetattr(stdin_fileno, tcsadrain, &term_current);

a simple read loop can read in data generated each button press so:

char c; while (read(0, &c, 1) != -1) { print_char(c); }

now,

  • pressing esc on keyboard generates: 0x1b.
  • pressing f1 generates: 0x1b 0x4f 0x50.
  • pressing f5 generates: 0x1b 0x5b 0x31 0x35 0x7e.

in terms of reading , processing input, how 1 determine output 1 button press ends , next 1 begins? find no discernible pattern, , fact esc generates single byte identical first byte of output multi-byte generating button presses seems suggest there none. there other mechanism determining button boundaries are?

programs rely on keys not being pressed fast. if delay less 100ms, 1 key press; otherwise there 2 separate events.

yes program pause time after esc being pressed, in order make sure it's esc , no other key. pause can discerned naked eye.

some programs recognize escdelay environment variable fine-tuning timing.

and yes not perfect, can fool system pressing keys fast.


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